<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button class="begin">开启定时器</button>
    <button class="stop">停止定时器</button>
    <script>
        var begin = document.querySelector('.begin');
        var stop = document.querySelector('.stop');
        var timer = null;
        begin.addEventListener('click', function() {
           timer =  setInterval(function() {
                console.log('你好吗？');
            }, 1000);
        });
        stop.addEventListener('click', function() {
            clearInterval(timer);
        });

    </script>
</body>
</html>